Abstract

Standoff chemical detection with a distance of more than 41 feet using photoacoustic effect and quantum cascade laser (QCL) operated at relatively low power, less than 40 mW, is demonstrated for the first time. The option of using QCL provides the advantages of easy tuning and modulation besides the benefit of compact size, light weight and low power consumption. The standoff detection signal can be calibrated as a function of different parameters such as laser pulse energy, gas vapor concentration and detection distance. The results yield good agreements with theoretical model. Techniques to obtain even longer detection distance and achieve outdoor operations are in the process of implementation and their projection is discussed.

Dependence of PA signal on laser power (laser pulse energy). Laser pulse width is kept at 300 µs and repetition rate is 1.5 kHz. Detection distance is 15 ft. Laser power is measured as average output power of the QCL. Square: measurements; solid line: linear fit.